A plasma display panel (hereinafter referred to as “panel”) is a display device that has a large screen, is thin and light, and has high visibility.
A typical alternating-current surface discharge type panel used as the plasma display panel has many discharge cells between a front plate and a back plate that are faced to each other. The front plate has the following elements:                a plurality of display electrode pairs disposed in parallel on a front glass substrate; and        a dielectric layer and protective layer for covering the display electrode pairs.Here, each display electrode pair is formed of a scan electrode and a sustain electrode. The back plate has the following elements:        a plurality of data electrodes disposed in parallel on a back glass substrate;        a dielectric layer for covering the data electrodes;        a plurality of barrier ribs disposed on the dielectric layer in parallel with the data electrodes; and        phosphor layers disposed on the surface of the dielectric layer and on side surfaces of the barrier ribs.The front plate and back plate are faced to each other so that the display electrode pairs and the data electrodes three-dimensionally intersect, and are sealed. Discharge gas is filled into a discharge space in the sealed product. In the panel having this configuration, ultraviolet rays are emitted by gas discharge in each discharge cell. The ultraviolet rays excite respective phosphors of red, blue, and green, emit light, and thus provide color display.        
A subfield method is generally used as a method of driving the panel. In this method, one field time period is divided into a plurality of subfields, and the subfields at which light is emitted are combined, thereby performing gradation display. Here, each subfield has an initialization time period, a writing time period, and a sustaining time period.
In the initialization time period, initializing discharge is performed simultaneously in all discharge cells, the history of the wall charge for each discharge cell before the initializing discharge is erased, and wall charge required for a subsequent writing operation is formed. In the writing time period, scan pulse voltage is sequentially applied to the scan electrodes, writing pulse voltage corresponding to signals of images to be displayed is applied to the data electrodes, writing discharge is selectively raised between the scan electrodes and the data electrodes, and the wall charge is selectively formed. In the subsequent sustaining time period, a predetermined numbers of sustaining pulse voltages are applied between the scan electrodes and the sustain electrodes, and discharge and light emission are performed selectively in the discharge cells where the wall charge is formed by writing discharge. This method is described in “Whole plasma display”, by Hiraki Uchiike and Shigeo Mikoshiba, Kougyou Chosakai Publishing Inc., May 1, 1997, p79-p80, p153-p154, for example.
A driving method allowing suppression of false contours generated by the subfield method is also proposed (for example, Japanese Patent Unexamined Publication No. H11-305726). In this method, only one initializing operation and only one writing operation are performed in a plurality of subfields, thereby continuing subfields in which light is emitted and suppressing the false contours.
In the driving methods discussed above, operations in the initialization time period, writing time period, and sustaining time period are executed by time division, and respective times required for the initializing operation, the writing operation, and the sustaining operation are summed. The driving time becomes therefore long. Therefore, the time assigned to the sustaining time period becomes short and sufficient luminance cannot be secured, or the time for increasing the number of subfields cannot be secured and the number of gradations to be displayed cannot be increased.
The present invention addresses the problems, and provides a driving method of a plasma display panel and a plasma display device. The method and device secure the time assigned to the sustaining time period or the time for increasing the number of subfields, and allow increase of luminance and high gradation display.